Tetraaryl-1, 4-bis(dicyano-methylene)cyclohexadienes and their dihydro derivatives



States Patent 3,408,367 TETRAARYL 1,4 BIS(DICYANO METHYL- EN E)CYCLOHEXADIENES AND THEIR DI- HYDRO DERIVATIVES Sam Andreades, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed July 12, 1965, Ser. No. 471,460 8 Claims. (Cl. 260-396) ABSTRACT OF THE DISCLOSURE Tetraaryl 1,4 bis(dicyanomethylene)cyclohexadienes (I) and their dihydro derivatives (II) are claimed. The electrolytic reductive dimerization of a dicyanomethylenecyclopropene yield II which is converted into I by oxidation. The cyclohexadienes I are useful as polymerization inhibitors and the dihydro derivatives are useful as intermediates to the cyclohexadienes.

Description of the invention This invention relates to a new class of chemicalcompounds and to their preparation, and more particularly, to tetraphenyl substituted and tetra(substituted phenyl) substituted 1,4-bis(dicyanomethylene)cyclohexadienes, and to their dihydro derivatives which are also known as tetraphenyl substituted and tetra(substituted phenyl) substituted l,4-bis(dicyanomethyl)benzenes.

The novel compounds of this invention may be represented by the formulae NC CN wherein R R R and K, may be alike or dilferent, with each having 6-18 carbon atoms and being phenyl or phenyl substituted with 1-4 substituents selected from the group consisting of halogen (fluorine, chlorine, bromine or iodine), nitro, alkyl, alkoxy, each of which has 1-12 carbon atoms, and NR R wherein R and R may be alike or diiferent and are hydrogen or alkyl of 1-12 carbon atoms. Further, the substituents on the aforesaid phenyl group may be ortho, meta or para to the valence bond by which the phenyl group is attached to the carbocyclic diene or aromatic ring, with the provisos that iodo and alkyl substituents only may be meta or para, and only one substituent may be ortho. In the preferred embodiments of this invention R R R and R are either phenyl or monoalkyl substituted phenyl, with said alkyl substituent having 1-6 carbon atoms.

The dihydro compounds of this invention, i.e., the 1,4- bis(dicyanomethyl)benzenes, are prepared by an electrolytic reductive dimerization of a 1,2-disubstituted-3-dicyanomethylenecyclopropene, said 1,2-substituents being as defined hereinabove for R to R The cathode potential during the electrolysis must be sufficiently negative to reduce the methylenecyclopropene, but not so low as to cause decomposition of the solvent or electrolyte employed. Hence, although cathode potentials more negative than 2.0 volts are operable, most generally cathode potentials of 0.9 to -2.0 volts (S.C.E.) are employed. Preferably, to minimize undesirable side reactions the cathode potential is maintained in the range '1.5 to

1.7 volts (S.C.E.). The cathodic material may be selected from a wide variety of substances, although platinum or mercury is preferred herein. The reductive dimerization generally is carried out under ambient conditions of temperature and pressure, i.e., at room temperature of about 25 C. and at about atmospheric pressure. Temperatures of 50 to C. are operable, however, and subatmospheric as well as superatmospheric pressures can be employed. The electrolytic reduction can be carried out with or without a cell-dividing membrane to separate the cathode and anode compartments. In an undivided cell the anode may be comprised of any material which is compatible with the reaction conditions. Platinum, gold, copper or carbon usually is employed. Preferably, the process is carried out in a divided cell with a mercury cathode, and an unfused Vycor salt bridge tube is used. The solvent utilized in the electrolysis should be stable to relatively large negative and positive potentials. Operable solvents include dimethylformamide, dimethylacetamide, nitromethane and acetone. The preferred solvent is acetonitrile since it not only exhibits the requisite stability but it is an excellent solvent for the appropriate electrolyte and reactants employed herein. The electrolyte, likewise, should be chosen from materials which are stable under reaction conditions. Examples of operable electrolytes include tetraethylammoniurn percholorate, tetrabutylammonium perchlorate and tetrapropylammonium-p-toluenesulfonate. The amount of current passed during the reductive electrolysis should be about one fara-.

day per mole of reactant although excess or insufficient current may be employed. Cosolvents, although not necessary, may be utilized, and preferably aprotic solvents. The product of the electrolytic reaction is the dianion of a tetraphenylor tetra-(substituted phenyl)-1,4-bis(dicyanomethyl)benzene. Protonation of this material is achieved by acidification of the reaction mixture. Finally, the dihydro compounds of this invention are converted to the quinodimethan structure by oxidation, e.g., with chlorine as shown in Example III, or electrochemically. In the latter type process the oxidation is carried out at a cathode potential in the range 0.2 to +0.8 volt (S.C.E.). Voltages in'excess of 0.8 volt, although opperable, provide undesirable side reactions. Moreover, voltages more negative than 0.2 volt, although operable, provide a sufficiently reductive environment that the quinodimethan is reduced to its anion radical (discussed hereinbelow). The optimum and preferable oxidation cathode potential required to minimizze the aforesaid side reactions is in the range +0.25 to +0.35 volt.

The dicyanomethylenecyclopropenes utilized as reactants in the electrolytic reductive dimerization of the present invention are claimed in co-pending co-assigned application, Ser. No. 410,747, filed Nov. 12, 1964, now U.S. Patent 3,366,664.

The following examples are intended to illustrate but not limit the products and process of this invention.

EXAMPLE I 1,4-bis(dicyanomethyl)-2,3,5,6-tetraphenylbenzene HON NCHCN A solution of 100 mg. of l,2 diphenyl-3-dicyanomethylenecyclopropene and 2.2 g. of tetraethylammonium perchlorate in 100 ml. of acetonitrile is electrolytically reduced using a stirred mercury pool cathode at a potential of 1.70 volts (S.C.E.). The cell is divided by using an anode contained in an unfused Vycor chamber. A drop in current flow is noted when the number of fardays passed is equivalent to the amount of starting material (assuming a one electron per molecule reduction), indicating that the reduction proceeds with 100% current efiiciency. The reaction is discontinued and the reaction mixture is evaporated to dryness, taken up in 100 ml. of distilled water and filtered to give 56 mg. of an intractable solid. The filtrate, which is alkaline, is acidified with one drop of concentrated hydrochloric acid. The yellow precipitated solid which is removed by filtration and dried weighs 55.1 mg. and is identified as 1,4-bis(dicyanomethyl)-2,3,5,6-tetraphenylbenzene, also known as tetraphenyldihydrotetracyanoquinodimethan or tetraphenyldihydro-TCNQ. The product contains some tetraphenyltetracyanoquinodimethan as shown by the nitrile bands appearing at 4.4 1 and 4.5,u in the infrared spectrum (KBr disc). An analytical sample is obtained by recrystallization from acetonitrile.

Analysis.Calcd. for C H N C, 84.68; H, 4.34; N, 10.98; mol. wt. 510. Found: C, 83.90; H, 4.48; N, 10.98; mol. wt. 510, 10.74.

The molecular weight is determined by direct introduction of the sample into the isatron of a mass spectrom' eter.

The 56 mg. of intractable solid recovered above is a mixture of tetraphenyltetracyanoquinodimethan and an unidentified material. Oxidation of the solid with chlorine yields unstable orange crystals believed to be 1,4-bis- (chlorodicyanomethyl)-2,3,5,6-tetraphenylbenzene which decomposes on attempted recrystallization.

EXAMPLE II Example I is repeated using a platinum cathode. From this example is recovered 31 mg. of tetraphenyldihydrotetracyanoquinodimethan. Recrystallization of the product from 1.0 ml. of acetonitrile gives 7 mg. of white crystals, M.P. 329332 C. (dec., sealed capillary). The infrared spectrum is identical to that of the product of Example I and exhibits both aromatic and aliphatic C-H stretching, based upon absorption bands at 323 and 3.41 1, and weak CN, based upon absorption at 4.4 4; ad ditional bands are noted at 6.25, and 6.32,u.

EXAMPLE III 2,3,5,6-tetraphenyl-7,7,8,8-tetracyanoquinodimethan A solution of 25 mg. of tetraphenyldihydrotetracyanoquinodimethan in 10 ml. of acetonitrile containing one drop of triethylamine is oxidized by passing an excess of chlorine gas through the solution at room temperature. The immediate formation of a yellow color is observed. After 5-10 minutes the introduction of the chlorine gas is discontinued and the solution is evaporated to dryness to give 24.2 mg. of orange crystals of 2,3,5,6-tetraphenyl-7,7,8,8-tetracyanoquinodimethan. The infrared spectrum shOWS nitrile absorption at 4.5 1. and a strong absorption band at 6.73n. Recrystallization of the product from 0.8 ml. of acetonitrile gives an analytical sample of 11 mg. of orange-red crystals, M.P. 3l8-320 C. (dec., sealed capillary). The infrared spectrum for this material (KBr pellet) shows neither aliphatic nor aromatic C-H stretching absorption; bands are noted at 6.3g, 6.7g, and 6.9

Analysis.-Calcd. for C H N C, 85.02; H, 3.96; N, 11.02; mol. wt. 508.54. Found: C, 84.74; H, 4.45; N, 11.26; mol. wt. 508 (mass spec, direct introduction).

The ultraviolet spectrum of this product in acetonitrile shows a X at 450 mn (e=25,000), with a broad absorption at 600 m (6: 14,800). A shoulder running into end absorption is noted at 310 mm. For comparison, the ultraviolet spectrum of tetracyanoquinodimethan exhibits a )t at 395 m (e=63,000). The ulartviolet spectrum illustrates the utility of this class of compounds as ultraviolet absorbers. Further, the ultraviolet spectrum exhibits a band at 890 mn, indicating the presence of a small quantity of tetraethylammonium tetraphenyltetracyanoquinodimethanide, an anion radical salt formed by the partial chemical oxidation of the dihydro compound. The electrolytic preparation of the anion radicals is described below.

EXAMPLE IV Example I is repeated using in place of the 1,2-diphenyl-3-dicyanomethylenecyclopropene one of the substituted cyclopropenes shown below. In each instance the recovered dihydro product is oxidized to the tetracyanoquinodimethan according to the procedure of Example III. In each of the four experiments R and R are the same and appear in both the reactant and the products.

REACTANT PRODUCTS NC CN NC H CN NC CN H Y A Ri R2 R- R R1 1 2 l I R1- -R, R1 R2 /l\ A NO ON As indicated above, the preceding examples are illustrative only. Shown below in Table I are additional substituted cyclopropenes which are operable in this invention. It is obvious that mixtures of substituted cyclopropenes likewise may be electrolytically reductively dimerized to give mixtures of products. In such a mixture of reactants either substituted cyclopropene may couple with itself or with another substituted cyclopropene present in the mixture. Moreover, even where'a single disubstituted cyclopropene is employed in the dimerization reaction mixtures of products also will be obtained if the substituents on each aryl group are dissimilar. It is to be understood, therefore, that any of the R groups depicted in Table I, i.e., R R R or R may be alike or different. In most cases, because of preferable preparative feasibility R R R and R; will be the same. Although only the dihydro products are shown in Table I, in each case the tetracyanoquinodimethan may be obtained by oxidation of the dihydro compound as illustrated in Example III.

Q-cmcnm (|)OHa F OCHa NC CN III wherein each of R R R and R is as defined hereinabove. The instant discovery provides the first known evidence of anion radicals which are derived from tetraphenyland tetra(substituted phenyl) tetracyanoquinodimethans. Previously, only unsubstituted 7,7,8,8-tetracyanoquinodimethan, or alkyl substituted derivatives thereof, were known to be convertible to anion radical salts. In addition to the aforesaid reference this prior art disclosure is made in US. Patent 3,115,506, issued Dec. 24, 1963 to Acker et a1. Further, as to the prior art, Weitz and Schmidt, Berichte, 75, 1921 (1942), have reported the conversion of tetraphenylquinodimethan to a cation radical. Finally, it is worthy of note with regard to the prior art on quinodimethans generally that their syntheses differ markedly from the process of the instant invention. Thus, although di-n-propyldicyanomethylenecyclopropene is known [Kende et al., J. Am. Chem. Soc., 86, 3588 (1965)], it is believed never to have been employed in the preparation of prior art alkyl substituted quinodimethans. Moreover, the unsubstituted dicyanomethylenecyclopropene which would be required for the synthesis of unsubstituted quinodimethans, employing the present process, is believed to be unknown in the prior art, a fact which probably is related to its inherent instability and/ or difficulty of isolation.

The formation of the aforesaid anion radicals from the quinodimethans of the instant invention may be effected by a variety of means. As may be seen from Example III the chlorine oxidation of the dihydro compound provides some anion radical as an intermediate in the quinodimethan synthesis. Preferably the dihydro compound is oxidized completely to the quinodimethan and the latter is partially reduced to the anion radical, either by chemical or electrolytic means. Thus, treatment of the quinodimethan with an approximately stoichiometric quantity of a metal iodide, such as potassium iodide, in an appropriate solvent, such as acetonitrile, yields the anion radical. Alternatively, the quinodirnethan may be electrolytically reduced under the same environmental conditions previously described except that the cathode potential is maintained within the range 0.6 to +0.4 volt (S.C.E.). Preferably the reduction is effected at a cathode potential in the range of 0.05 to-0.15 volt. The current is passed during the reduction until it diminishes to 1% of its initial value. As an example of the electrochemical generation of the anion radical, Example I is repeated carrying out the reductive coupling reaction on 100 mg. of 1,2-diphenyl- 3-dicyanomethylenecyclopropene and 2.2 g. of tetraethylammonium perchlorate in 100 ml. of acetonitrile using a stirred mercury pool cathode at a potential of about 1.70 volts (S.C.E.) To elfect an electrochemical oxidation the potential then is increased to about +0.3 volt and current passage is continued until another faraday per mole of starting material is consumed, after which the potential is maintained at about 0.1 volt until the current drops to 1% of its initial value at 0.1 volt. The resultant solution which contains the tetraethylammonium salt of the anion radical in a solvated stabilized form exhibits a strong 9- line electron spin resonance spectrum indicative of the tetraphenyltetracyanoquinodimethan anion radical: 4 equivalent nitrogens (A ='1.08:0.01); g=2J00265 10.003 A 13 splitting is observed and attributed to four C atoms, three of which are equivalent (A 13='9.5Oe). The ultraviolet spectrum of the acetonitrile solution exhibits a A at 890 indicative of the anion radical.

The tetraphenyl and tetra(substituted phenyl) tetracyanoquinodimethans of this invention are unique in that their aromatic moieties are susceptible to electrophilic substitution reactions. Hence, although the prior art tetracyanoquinodimethans, when chlorinated in the presence of iron, yield 1,6-addition products, namely, 1,4-bis(chlorodicyanomethyl)benzenes, phenyl ring chlorination occurs with the compounds of the instant invention when chlorination is carried out under similar conditions.

As demonstrated by Example III, the tetra substituted tetracyanoquin-odimethans of this invention are useful as ultraviolet absorbers. It has been noted that said compounds likewise exhibit utility as polymerization inhibitors. Thus, when a sample of purified acrylonitrile containing a trace quantity of azobisdiisobutyronitirle is refluxed for -15 minutes, rapid polymerization occurs; whereas, when purified acrylonitrile containing not only a trace quantity of the azobisdiisobutyronitrile but a trace quantity of e.g., tetraphenyltetracyanoquinodimethan is refluxed for 5-15 minutes, no polymerization is evident. Finally, the tetraphenyl and tetra (substituted phenyl) tetracyanoquinodimethans of this invention are useful in thermographic copying papers. The thermographic process for copying of printed or written records uses a copy sheet bearing a substantially colorless coating which darkens on heating. When such a sheet is placed in contact with a text-bearing master and the assembly is exposed to a source of radiant heat, the portions of the copy sheet in register with text areas, particularly where they contain carbon, are heated much more rapidly than portions in register with blank areas of the master. The copy sheet is darkened only in those areas in register with text areas of the master and a copy is obtained. The color change in the copy sheet must take place at a temperature which otherwise causes no change in the copy sheet or master. The tetracyanoquinodimethans of this invention are useful as an active ingredient of the coating applied to the thermographic copy sheet.

The foregoing detailed description has been given for clearness of understanding only and no unnecessary limitations are to be understood therefrom. The invention is not limited to the exact details shown and described, for obvious modifications will occur to those skilled in the art.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A compound of the formula NC CN NC CN wherein R R R and R each contains 6-18 carbon atoms and is selected from the group consisting of phenyl and phenyl substituted with 1-4 substituents, each of which is selected from the group consisting of fluorine, chlorine, bromine, iodine, nitro, alkyl, alkoxy and NR R wherein each of said alkyl and alkoxy substituents contains 1-12 carbon atoms and each of R and R is selected from the group consisting of hydrogen and alkyl of 1-12 carbon atoms, with the provisos that iodo and alkyl substituents on said substituted phenyl are in a position selected from the group consisting of the meta and para positions, and the number of ortho substituents on said substituted phenyl is less than 2.

2. The compound of claim 1 wherein each of R R R and R is phenyl.

3. A compound of the formula WNM R1 Ra Ra- R4 ('irnoNh wherein R R R and R each contains 6-18 carbon 8 i atoms and is selected from the group consisting of phenyl and phenyl substituted with 1-4 substituents, each of which is selected from the group consisting of fluorine, chlorine, bromine, iodine, nitro, alkyl, alkoxy and NR R wherein each of said alkyl and alkoxy substituents contains 1-12 carbon atoms and each of R and R is selected from the group consisting of hydrogen and alkyl of 1-12 carbon atoms, with the provisos that iodo and alkyl substituents on said substituted phenyl are in a position selected from the group consisting of the meta and para positions, and the number of ortho substituents on said substituted phenyl is less than 2.

4. The compound of claim 3 wherein each of R R R and R is phenyl.

5. A potassium salt of the anion radical of the formula N C C N R1 Ra AK N C C N said anion radical being in a stabilized solvated form as a solution in acetonitrile, and wherein R R R and R each contains 618 carbon atoms and is selected from the group consisting of phenyl and phenyl substituted with 1-4 substituents, each of which is selected from the group consisting of fluorine, chlorine, bromine, iodine, nitro, alkyl, alkoxy and NR R wherein each of said alkyl and alkoxy substituents contains 1-12 carbon atoms and each of R and R is selected from the group consisting of hydrogen and alkyl of 1-12 carbon atoms, with the provisos that iodo and alkyl substituents on said substituted phenyl are in a position selected from the group consisting of the meta and para positions, and the number of ortho substituents on said substituted phenyl is less than 2.

6. A compound of claim 5 wherein each of R R R and R is phenyl.

7. A quaternary ammonium salt of the anion radical of the formula said anion radical being in a stabilized solvated form as a solution in acetonitrile, and wherein R R R and R each contains 6-18 carbon atoms and is selected from the group consisting of phenyl and phenyl substituted with 1-4 substituents, each of which is selected from the group consisting of fluorine, chlorine, bromine, iodine, nitro, alkyl, alkoxy and NR R wherein each of said alkyl and alkoxy substituents contains 1-12 carbon atoms and each of R and R is selected from the group consisting of hydrogen and alkyl of 1-12 carbon atoms, with the provisos that iodo and alkyl substituents on said substituted phenyl are in a position selected from the group consisting of the meta and para positions, and the number of ortho substituents on said substituted phenyl is less than 2.

8. A compound of claim 7 wherein each of R R R and R is phenyl.

References Cited UNITED STATES PATENTS 3,1l5,506 12/1963 Acker et a1 260396 LORRAINE A. WEINBERGER, Primary Examiner.

L. A. THAXTON, Assistant Examiner. 

